A standard central motor-vehicle lock system has a plurality of door latches on the individual doors, hatches, trunk lids, and the like that are each operable by a respective power actuator and also by a manual mechanism. The power actuator can include a hydraulic, pneumatic, or electric motor, and the manual mechanism is almost always a lever linkage. All of the actuators can be operated centrally, normally from the driver's seat or door, to lock and unlock the doors.
It has become common to provide such a central locking system with a so-called antitheft feature. When set in the antitheft mode it is impossible to unlock the vehicle doors even by manual actuation of the latches. Thus a person who breaks a window or otherwise gains forcible entry to the vehicle cannot open its doors.
Such a system as described in my earlier U.S. Pat. No. 4,669,283 uses an actuator constituted as a housing in which is displaceable a slide connected to the respective inside door-locking element, normally a knob. This slide in turn is displaced by means of a nut which rides on a threaded spindle rotated by the respective motor. The slide is displaceable between an unlocked, a locked, and an antitheft position. The nut engages a deflectable part of the slide to displace it into the locked and unlocked positions so that when in these positions the setting can be manually overridden. On the other hand, the nut positively engages a wall of the slide in the antitheft position. The gear train driving the spindle, the types of threads employed between the nut and the spindle, or similar means are employed to make it impossible to move the slide when thus held in the antitheft position without actually destroying the actuator. Clearly such an arrangement requires that the actuator be made very strong in order to give the greatest level of security. This requires typically that very robust parts be used, thereby increasing the size, weight, and cost of the assembly, or that binding-type threads be employed between the spindle and nut so that a relatively strong motor be used or a relatively slot actuation must be allowed for.
In another known arrangement described in commonly owned U.S. Pat. No. 4,342,209 a separate latch dog is employed on the slide that engages in a keeper in the housing of the actuator in the antitheft position. Such an arrangement is relatively secure, but once again is fairly complex and expensive to manufacture.